The long-term goal of this project is to gain an improved understanding of the influence of aging on balance function so that elderly persons with disequilibrium can be managed more effectively. Because balance function is known to depend in large part on both visual and vestibular function, this study will evaluate the effect of aging on a well established vestibulo-ocular phenomenon, velocity storage. Elderly persons will be tested to assess the vestibulo-ocular and visuo-ocular reflexes including responses of both the semicircular canals and otolith organs of the vestibular system and the response to moving visual stimuli. The specific aims of this study are to test several hypotheses that pertain to the effect of aging on velocity storage. The vestibulo-ocular and visuo-ocular reflexes of young adults will be tested for comparison to the responses of the elderly individuals. Vestibular stimulation will be accomplished using computer controlled rotation about an earth vertical axis and about an off-vertical axis. Visual stimuli will include precise movements of full-field optokinetic stripes. Several pairwise interactions of the vestibular and visual stimuli will be recorded to evaluate "charging" and "dumping" of velocity storage. The information provided from this study will improve our understanding of the effect of the aging process on vestibular function and will have implications regarding sensory-motor transformation and sensory-sensory interactions.